CROSS-REFERENCE TO RELATED APPLICATIONS
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
BACKGROUND OF THE INVENTION
[0003] The present invention relates to data transmission, and more particularly to a method
and apparatus for transparently embedding data within a video signal in order to indicate
authentication, program ownership and/or reception-verification of the video signal.
[0004] Television signals are usually copyrighted or otherwise proprietary to the originator
and, in the case of television network distribution, are distributed to affiliate
stations for re-broadcast. Unauthorized re-broadcast is difficult to detect since
it is often difficult to determine the creator or originator of the material from
the material itself. This is particularly true for short sequences or when the video
image has been cropped or modified to mask any identification logos that may have
been explicitly burned into the video image.
[0005] Another common problem with television and video distribution, which is becoming
more severe, is the synchronization of an aural or audio component that is to be distributed
with the video signal. Modern digital signal processing techniques requiring large
buffering, such as MPEG compression, add latency to the video distribution and, since
the audio may be distributed or processed separately, an error in audio to video "lip-sync"
or in sound to action often occurs. Sometimes this latency is variable, requiring
continual re-synchronization. In addition to audio to video synchronization problems,
the audio signal may be distorted or missing entirely. By embedding, for example,
the audio envelope as data within the video signal, it is also possible to detect
and compare the received audio with the original which was coded and embedded as data
within the video signal as a quality measure as well as video to audio delay.
[0006] Another problem is with authentication of video signals representing visual images,
possibly created by a computer, where it is desirable to detect a forgery or imposter
signal. In this case the video signal may be replicated to such a degree that it is
difficult to detect it from the authentic video sequence. Also it is sometimes desirable
to detect the beginning and/or ending of a particular sub-sequence of a video signal,
such as a motion test sequence for in-service video quality assessment of video processed
by MPEG compression. It is possible to devise a remote receiver to capture a special
test sequence segment of a distributed video signal and compare that segment to an
undistorted, stored version to assess the quality of the video. Although it is possible
to uniquely and reliably detect when the sequence occurs so that it, and only it,
is captured, this generally requires the advance processing of a signature vector,
transmission of that vector through a separate channel and a correlation means at
the receiver. By transparently embedding data into the video a predetermined start
and end code may be detected by the receiver without any preloading of signature vectors
and signature vector preprocessing.
[0007] Published Canadian Patent Application No. 2,174,413 (A1) by Geoffrey B. Rhoads entitled
"Identification/Authentication Coding Method and Apparatus" discusses techniques for
providing authentication of image signals. In Rhoads an imperceptible N-bit identification
code is embedded throughout an image with a small noise pattern in a coded fashion.
In particular bits of a binary identification code are referenced sequentially to
add up to N independent, noise-like patterns to the original image signal. The detection
of these patterns is done by N sequential correlations with stored replicas of each
pattern. This may also be done simultaneously by N correlators, as is well described
in the public domain as a "correlation receiver." Rhoads further discloses adding
or subtracting exactly N independent, noise-like images to improve detection and/or
encoded image quality. This later modification, referred to by Rhoads as "true polarity",
is well described in the public domain as "bi-orthogonal signaling" for a correlation
receiver allowing 2^N composite symbols (patterns) to be created by adding or subtracting
N bi-orthogonal symbols (patterns). A disadvantage of both of Roads' methods is that
each of the N noise-like patterns, which are added or subtracted to form one of the
2^N possible composite patterns, needs to be properly scaled and designed to minimize
image degradation by the addition of the composite pattern to the image. A further
disadvantage is that the original unencoded image, as well as the N patterns, need
to be stored in the receiver so that the unencoded image may be subtracted from the
encoded image for detection.
[0008] U.S. Patent No. 4,969,041 issued November 6, 1990 to William J. O'Grady and Robert
J. Dubner entitled "Embedment of Data in a Video Signal" discloses adding one of a
plurality of low-level waveforms to the video signal, with the level of the low level
waveform being below the noise level of the video signal, for authentication purposes
or for transmitting information. Each low-level waveform corresponds to a particular
data word being embedded. At the receiving end the video signal is correlated with
an identical set of low-level waveforms to produce a set of correlation coefficients
-- the highest correlation coefficient indicating the presence of a particular one
of the low-level waveforms which is then converted into the corresponding data word.
The Rhoads composite pattern consists of the summation of up to N independent patterns,
which would be the same as O'Grady/Dubner when N=1 since only one pattern is sent
at a time. For an N-bit data word O'Grady/Dubner implies the need for storage of 2^N
patterns rather than the N patterns of Rhoads. But since 2^N patterns may be generated
by summing N bi-orthogonal sub-patterns, the effect is the same and only N patterns
need to be stored in a manner identical to Rhoads. In both of these patents the symbol
rate is one pattern per picture or field.
[0009] Some other drawbacks of O'Grady/Dubner are that it limits the degree to which a pattern
or sequence of patterns can be hidden by not fully exploiting the limitations of the
human psychovisual process, such as spatial masking; it does not fully exploit the
available signal to noise ratio since the correlation output is unipolar; and it does
not include coding of the data represented by the embedded symbols so as to provide
temporal redundancy for error correction over missing video frames.
[0010] What is desired is a method of embedding an unobtrusive data pattern into the video
signal that is useful in addressing the above-noted problems.
BRIEF SUMMARY OF THE INVENTION
[0011] Accordingly the present invention provides a method and apparatus for transparently
embedding data into a video signal by modulating a particular carrier frequency with
a randomized pattern representing the data. The randomized pattern may be a combination
of the data with the output from a pseudo-random binary sequence generator, or the
data may be converted first into a bi-orthogonal pattern selected from among a plurality
of such patterns and then randomized. The resulting modulated carrier frequency is
then amplitude modulated based upon a human visual model so that the modulated carrier
frequency amplitude is greater in areas of high image complexity and lower in areas
of low image complexity. The subliminal data represented by the modulated carrier
frequency is added to the video signal. At a decoder the data is recovered using appropriate
correlation techniques by first filtering the video signal to increase the subliminal
data component relative to the image component, then demodulating the data component
to produce the data pattern, and then correlating the data pattern with the possible
data patterns to identify the particular pattern and associated data word.
[0012] The objects, advantages and other novel features of the present invention are apparent
from the following detailed description when read in conjunction with the appended
claims and attached drawing.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
[0013] Fig. 1 is a block diagram view of an encoder for transparently embedding data in
a video signal according to the present invention.
[0014] Fig. 2 is a block diagram view of a feedback model for determining parameter values
for a human visual model according to the present invention.
[0015] Fig. 3 is a block diagram view of a decoder for extracting embedded data in the video
signal according to the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0016] The invisibility of embedded data in a video signal is achieved by several independent
factors acting together. The first factor is the principle of spectral spreading from
Direct-Sequence Spread Spectrum (DSSS) modulation of a carrier frequency. The low-bandwidth/low-rate
data patterns or symbols are modulated by a higher rate Pseudo Random Binary Sequence
(PRBS), spreading the power spectrum around the carrier frequency so that the time-domain
waveform appears noise-like or lacks the spatial coherence that the eye/brain is good
at seeing even at low levels. Also by careful selection of the carrier frequency and
phase it is possible to further reduce the visibility of the resulting spatial pattern
created by the PRBS modulated symbols (patterns) on a DSSS modulated carrier.
[0017] Secondly it is also desirable to filter the embedded signal both vertically and horizontally
to reduce edge visibility, further enhancing it's overall invisibility. A third factor
that is significant is to exploit visual masking by varying the data signal level
according to the video content.
[0018] Another factor is the selection of a Field Alternate Carrier (FAC) frequency and
phase which becomes the DSSS modulated carrier. The invisibility of this carrier is
a function of it's frequency, but it's phase from one field to the next is very important.
A first-order cancellation occurs by repeating the entire data pattern on the even
field (field 1) again on the odd field (field 2), but with an inverted carrier phase,
causing an interlaced line pair cancellation. By repeating the data in each field,
an even-line field comb filter may be used in a decoder to cancel the field to field
correlated video and recover the data pattern with a 3 dB advantage at a cost of a
50% data-rate penalty. For progressive scan video systems the Field Alternate Carrier
frequency and data repeat may be replaced by a Line Alternate Carrier frequency and
data repeat. This gives the same or better visual cancellation and has the same data
rate as the interlaced scan system.
[0019] With video signals the decoder is greatly simplified since carrier, code and data
lock are simply derived from the abundant timing information in sync and burst. In
addition to the rejection afforded by the comb filter, a bandpass filter is used to
suppress the large carrier components of the program video signal. After the PRBS
correlation, or de-spreading, various detection methods are possible. An integrate
and dump matched filter driving a software, bi-orthogonal M-ary scheme may be used.
Two options with and without channel coding also may be used. Numerous alternatives
include combining convolution coding with Walsh code assignments (Ungerboech TCM)
and concatenated RS and convolution.
[0020] Channel coding is best done in a holographic, two-dimensional (2D) sense by shuffling
or the like for robustness against video motion of pixel segments passed through the
comb filter. Such 2D holographic shuffling of data may be extended to three-dimensional
(3D) shuffling because video has a time sense unlike still pictures. This may be done
by repeating some of the data over several frames, which could be valuable for video
sequence identification. The data that identifies the video sequence may be given
a lower energy, i.e., fewer pixels, than the data that identifies the particular frame
within the video sequence, since the frames come only once while the sequence has
many frames in it. Data security through data encryption may always be applied separately
from the channel coding, allowing the decoder design to be public or even standardized.
[0021] Referring now to Fig. 1 an encoder
10 is shown having an analog video signal which is input to an anti-aliasing, lowpass
filter
12, the output of which is input to a sync/burst separator
14 to generate necessary timing signals and to an analog to digital converter (ADC)
16 to product a digital video signal. A sample clock phase locked loop (PLL)
18 in response to one of the timing signals (subcarrier frequency fsc) from the sync/burst
generator
14 provides a sample clock at four times subcarrier (4fsc). Where the input signal is
a digital video signal, the timing signals are extracted from the digital video signal
and the lowpass filter
12 and ADC
16 are not needed. The digital video signal is input to an adder
20 where a subliminal data signal is added to the digital video signal. The resulting
digital video signal is input to a digital to analog converter (DAC)
22 to produce a modulated analog video signal which in turn is processed by an output
lowpass reconstruction filter
24 to produce a final encoded analog video signal. For digital distribution the DAC
22 and filter
24 may be eliminated.
[0022] A modulator circuit
30 generates the subliminal data signal for input to the adder
20. The modulator circuit
30 has as inputs the vertical and horizontal timing signals from the sync/burst separator
14 and the desired subliminal data to be added to the digital video signal. The subliminal
data is input to a circular shift register
32 which has as inputs the horizontal and vertical sync signals. The subliminal data
from the circular shift register
32 may be input to an exclusive OR gate
34 where it is combined with the output from a pseudo random binary sequence (PRBS)
generator
34. The PRBS generator
34 is reset by the vertical sync signal and clocked by a clock signal derived via a
local PLL
36 and a divider
38. The output from the exclusive OR gate
35 is a series of +/-1's which is then input to a mixer
40. A numerically controlled oscillator (NCO)
42 provides a modulator frequency fo that also is input to the mixer
40. The output from the mixer
40 is a modulated frequency signal which is the DSSS signal as modulated by the output
from the PRBS generator
34 and the data from the circular shift register
32.
[0023] To provide the Field Alternate Carrier frequency an inversion of the phase of either
of the inputs to the modulator
40 is performed using a divide-by-two circuit
37 having the vertical interval timing signal as an input followed by another exclusive
OR gate
39. The exclusive OR gate
39 has as shown the other input coupled to the output of the first exclusive OR gate
35, the output being coupled to the modulator
40. Alternatively the exclusive OR gate
39 may be inserted between the NCO
42 and the modulator
40, between the circular shift register
32 and the first exclusive OR gate
35, or between the PRBS generator
34 and the first exclusive OR gate. For progressive scan systems the input to the divide-by-two
circuit
37 would be the horizontal interval timing signal so that the Line Alternate Carrier
frequency is implemented. In either case alternate lines in each complete frame of
the video image sequence have the same data, but inverted in phase, so that subtraction
of alternate lines by a comb filter in a decoder enhances the subliminal data signal.
[0024] The modulated frequency is input to two-dimensional, horizontal and vertical spatial
frequency, softening filters
44. The horizontal filter
44A is centered about the modulator frequency fo to mitigate any fast edges in the modulated
frequency signal, and the vertical filter
44B mitigates fast vertical edges (line-to-line transitions). The modulated frequency
signal is the subliminal data signal that is input to the adder
20 via a blanking gate
46 so that the addition occurs only during the active video portion of the digital video
signal.
[0025] A human vision model (HVM) circuit
48 has as inputs the digital video signal at the input to the adder
20. One practical implementation of visual masking based upon the human visual model
is shown. A first aspect of the human visual model is noise tolerance in areas of
high spatial detail, and this is controlled by a two-dimensional highpass filter
41, such as a Sobel filter, followed by an envelope squarer
43 and a first control amplifier
45. A second aspect is sensitivity to noise at different local contrasts, and this is
controlled by a two-dimensional lowpass filter
47 followed by a transfer offset circuit
49 and a second control amplifier
51. The parameters A1 and A2 represented by the first and second control amplifiers
45, 51 are adjusted for a desired minimum data pattern visibility over a range of picture
material. A third aspect may be that of temporal masking
55 where noise on screen cuts or motion is temporarily less visible. The resulting outputs
from these paths, describing the complexity of the image rendered by the digital video
signal, are summed by a summer
53 to produce a gain signal to control a multiplier
50 to which the modulated frequency signal is input prior to the adder
20. Thus for portions of the digital video signal where the image is unchanging in motion
and/or has low spatial detail and contrast or color/shading variations, the gain is
relatively low; and where the image is complex due to motion and/or high spatial detail,
the gain is relatively high. In fact the amplitude of the subliminal data signal does
not need to be less than the noise floor in complex regions of the video digital signal
to retain an acceptable level of invisibility.
[0026] A feedback model
60 for determining the parameter values
A1, A2 represented by the first and second control amplifiers
45, 51 and the transfer curve of the transfer-offset circuit
49 is shown in Fig. 1. A desired or acceptable distortion value is pre-set and dynamically
maintained by feedback based on the human visual model. An image sequence is stored
in a video buffer
62 and repeatedly output in order to compare the output from the human visual model
64 prior to the encoder
10 with the image sequence derived from the output of the human visual model
66 following the data encoder. The comparison between the human visual model outputs
is performed by means of a means absolute difference or mean square error algorithm
68. The resulting difference or error is input to a comparator
69 to which also is input a distortion level which is adjustable to the desired level
of invisibility. The parameters of the first and second control amplifiers
45, 51 and the transfer curve of the transfer-offset circuit
49 are adjusted to maintain comparator
69 output high. This is repeated over a range of exemplary image sequences. This then
produces an acceptable estimate of these parameters which may be fixed for all video
to be encoded. The human visual model is only as elaborate as necessary to match the
dominant elements of the human visual system as it relates to the desired level of
masking.
[0027] This feedback model may also be used without the masking modulator
48 in an iterative manner to directly determine the pattern level gain signal for input
to the multiplier
50. In other words a vector or array of gain signal values, maximized for each pixel,
may be determined based on the human visual model feedback, optimizing the root mean
square (RMS) value of the embedded pseudo-noise pattern while maintaining the desired
level of distortion.
[0028] Forward error correction may be added to the modulator
30 by inputting the subliminal data to a forward error correction (FEC) circuit
52 prior to input into the circular shift register
32. This will provide error correction for bit or byte errors when the data from the
circular shift register
32 is input directly to exclusive OR gate
35. The FEC circuit
52 may use a bit-error correction code, such as Golay codes, as the forward error correction
algorithm to improve the data integrity for bit errors, or a more sophisticated channel
coding such as concantenated convolution and Reed-Solomon (RS) code may be used, as
is well known in the art. These coding techniques combined with bit shuffling provide
error correction across frames so that entire frames may be lost without any loss
in data. For example FEC
52 may be designed to provide RS word-error correction where each frame contains a coded
binary word of a fixed length of
m data bits, allowing missing words (frames) to be completely recovered from the redundancy
in adjacent words (frames). In this case the output from the circular shift register
32 may be input to an orthogonal pattern selector
54, such as a Walsh encoder, to produce the subliminal data coded to select one of a
set of orthogonal patterns input to the exclusive OR gate
35. Walsh codes are one-dimensional orthogonal sequences used in the well-known IS-95
Code Division Multiple Access wireless telephone standard. Also Walsh sequences are
the basis for a particularly well-known set of two-dimensional orthogonal patterns
called Haadamard patterns. Orthogonal patterns are those that, when correlated with
all other patterns in the set, produce a positive correlation coefficient for only
one of the patterns, with all of the other patterns producing a zero correlation coefficient.
Where each pattern represents m bits, a total of 2^m patterns are required and the
data from the circular shift register
32 acts as an address to the pattern selector
54. By using bi-orthogonal patterns only 2^(m-1) patterns or sequences are needed for
m bits. These patterns may be input directly to the mixer
40 without the need of exclusive OR gate
35, but the bi-orthogonal patterns or Walsh sequences may not all appear visually random,
which would make them more visible when added to the program video signal. However
when this pattern is exclusive OR'd with the PRBS generator output, the resulting
light pattern at the output of the modulator
40 becomes much more random in appearance and is difficult to distinguish from noise.
The resulting modulation is a randomized bi-phase modulation spreading the spectral
energy around the carrier. Circular shift register
32 allows the data or data pattern to be repeated on interlaced fields so that the visual
line pair cancellation and field comb data separator in the decoder may be used, as
described above.
[0029] A decoder
70 is shown in Fig. 3. The input section
72 is the same as for the encoder
10, having a lowpass anti-aliasing filter
74, a sync/burst separator
76 to generate the timing signals, a PLL
78 to generate the sample clock and an analog to digital converter
80 to produce the digital video signal. The decoder
70 also includes a Local Oscillator (LO) section
82 which includes a PRBS generator
84 with PLL
86 and divider
88 and a numerically controlled oscillator (NCO)
90 that produces the demodulation carrier frequency
fo. The outputs from the PRBS generator
84 and the NCO
90 are input to a mixer
91 to produce a pseudo random demodulated LO signal (BPSK -- Bi-Phase Shift Keyed) for
a down-converter mixer
102.
[0030] The digital video signal is input to preprocessing filters
92 that include a bandpass filter
94 centered at the modulator frequency and a high pass field-comb filter
96 including a field delay
98 and a subtractor
100. These filters remove much of the program video signal, enhancing the detection of
the subliminal embedded data signal. The field-comb filter
96 is particularly effective since the embedded data pattern is repeated with inverse
polarity on adjacent fields, doubling it's level at the filter output while the program
video signal that is correlated on adjacent fields is removed. The filtered digital
video signal is input to the down-converter mixer
102 and mixed together with the pseudo random modulated LO frequency signal. The resulting
baseband digital signal is input to a correlation/matched filter circuit
104.
[0031] The correlation/matched filter circuit
104 has as inputs the baseband digital signal and the horizontal and vertical interval
timing signals. The timing signals are input to an orthogonal pattern generator
106, such as a Walsh generator, that is comparable to that in the encoder
10. The timing signals are also input to a matched filter
108 to which also is input the baseband digital signal. The matched filter
108 includes an integrate and dump circuit
110 followed by a sampler
112. If the embedded data is only as bits encoded with an FEC channel code, as discussed
previously, matched filter
108 output may be converted to binary data by slicer
124 and input directly to FEC decoder
126 to output the decoded and error corrected subliminal data. In the case where the
data is coded as bi-orthogonal patterns, the output from the sampler
112 is input to a bi-orthogonal correlation receiver
114 that includes a correlation mixer
116 for each of the patterns produced by the pattern generator
106 so that the sampler output is correlated with each pattern. The outputs from the
correlation mixers
116 are integrated by respective integrators
118, the outputs of which are input to a maximum magnitude selector
120. Due to the orthogonality of the patterns only one of the outputs from the integrators
118 has a significant magnitude that is detected by the magnitude and magnitude polarity
selector
120 as one of the predetermined
m bit patterns or data words assigned to each pattern. These
m data words may have been FEC coded as described previously. In this case the error
corrector
126 is designed to correct word errors based upon the redundancy in other decoded data
words in order to correct data errors from missing video frames or from heavily distorted
embedded data patterns. The magnitude selector
120 detects not only the greatest magnitude, but the polarity of that magnitude to provide
an extra bit. In other words eight patterns represent three bits plus one bit for
the eight inverted patterns, providing m=4 bits.
[0032] The subliminal data channel provided by the present invention may be used for stamping
an identifying mark on a video sequence even if some of the video frames have been
lost or portions of video frames have been cropped or distorted through lossy compression/decompression
processing. The identifying mark may represent an audio signal or at least a signature
of the audio into the active video to allow a remote video receiver to compare the
audio signature with the received audio to automatically advance or delay the relative
audio to video timing to maintain sound to video synchronization as encoded at the
source. The subliminal data channel may represent modern cryptographic digital signature
authentication in the video. It may be used to identify a motion test sequence, or
portion thereof, to be captured for video quality assessment, such as discussed in
co-pending U.S. Patent Application No. 08/605,241 filed February 12, 1996 by Bozidar
Janko and David K. Fibush entitled "Programmable Instrument for Automatic Measurement
of Compressed Video Quality". The subliminal data channel also may be used to analyze
timeliness of service, i.e., did the video get aired at the desired time in its entirety?
[0033] Thus the present invention provides for transparently encoding data into a video
image by modulating a particular carrier frequency, providing interlaced field visual
masking with a unique one of 2^(m-1) bi-orthogonal patterns, the pattern representing
m bits, randomizing the pattern with a PRBS sequence to reduce visibility, amplitude
modulating the random pattern modulated carrier to further maximize embedded signal
amplitude and minimize visibility based on a human visual model exploiting visual
masking, and adding the resulting pattern modulated frequency signal to the video
such that the data is recoverable using appropriate correlation techniques.
1. An apparatus for transparently encoding data within a video signal comprising:
means for generating from the data to be encoded and video timing signals associated
with the video signal a randomized binary pattern;
means for modulating the randomized binary pattern onto a carrier frequency to produce
a subliminal data signal; and
means for combining the subliminal data signal with the video signal to produce an
output video signal having the data transparently encoded within the video signal.
2. The apparatus as recited in claim 1 further comprising means for alternating the phase
of the subliminal data signal on alternate lines of each frame of the video signal
such that each pair of contiguous lines has the same data but inverted in phase.
3. The apparatus as recited in claim 2 wherein the alternating means comprises:
means for dividing a specific one of the video timing signals by two to produce a
phase inversion control signal; and
means for inverting the phase of the subliminal data signal on alternate lines of
each frame in response to the phase inversion signal.
4. The apparatus as recited in claim 3 wherein for an interlaced version of the video
signal the specific one of the video timing signals is a field rate signal and for
a progressive scan version of the video signal the specific one of the video timing
signals is a line rate signal.
5. The apparatus as recited in claim 1 further comprising means for amplitude modulating
the subliminal data signal prior to the combining means with a gain signal based upon
a human visual model.
6. The apparatus as recited in claims 1, 2 or 5 further comprising means for softening
edges in the subliminal data signal prior to the combining means.
7. A method of transparently encoding data within a video signal comprising the steps
of:
generating from the data to be encoded and video timing signals associated with the
video signal a randomized binary pattern;
modulating the randomized binary pattern onto a carrier frequency to produce a subliminal
data signal: and
combining the subliminal data signal with the video signal to produce an output video
signal having the data transparently encoded within the video signal.
8. The method as recited in claim 7 further comprising the step of alternating the phase
of the subliminal data signal on alternate lines of each frame of the video signal
such that each pair of contiguous lines has the same data but inverted in phase.
9. The method as recited in claim 8 wherein the alternating step comprises the steps
of:
dividing a specific one of the video timing signals by two to produce a phase inversion
control signal; and
inverting the phase of the subliminal data signal on alternate lines of each frame
in response to the phase inversion signal.
10. The method as recited in claim 9 wherein for an interlaced version of the video signal
the specific one of the video timing signals is a field rate signal and for a progressive
scan version of the video signal the specific one of the video timing signals is a
line rate signal.
11. The method as recited in claim 7 further comprising the step of amplitude modulating
the subliminal data signal prior to the combining step with a gain signal based upon
a human visual model.
12. The method as recited in claims 7, 8 or 11 further comprising the step of softening
edges in the subliminal data signal prior to the combining step.
13. The method as recited in claim 7 further comprising the step of shuffling the data
two-dimensionally to provide channel coding.
14. The method as recited in claim 7 further comprising the step of shuffling the data
three-dimensionally to provide channel coding.
15. An apparatus for transparently embedding data within a video signal comprising:
a pattern generator having as inputs timing signals associated with the video signal
and the data to be embedded and producing as an output a randomized pattern signal;
a modulator having as inputs the randomized pattern signal and a carrier frequency
synchronized with the randomized pattern signal and producing as an output a subliminal
data signal; and
a combiner having as inputs the subliminal data signal and the video signal and producing
as an output a transparently embedded data video signal.
16. The apparatus as recited in claim 15 further comprising a phase alternator circuit
having as inputs a specific one of the video timing signals and a component of the
subliminal data signal and having as an output a signal that produces inversion of
the phase of the subliminal data signal on alternate lines of each frame of the video
signal such that each pair of contiguous lines has the same data but inverted in phase.
17. The apparatus as recited in claim 16 wherein the phase alternator circuit comprises:
a divide-by-two circuit having as an input the specific one of the video timing signals
and having as an output a phase inversion control signal; and
an exclusive OR gate having as inputs the phase inversion control signal and the component
of the subliminal data signal and having as an output the signal for inverting the
phase of the subliminal data signal.
18. The apparatus as recited in claim 17 wherein for an interlaced version of the video
signal the specific one of the video timing signals is a field rate signal and for
a progressive scan version of the video signal the specific one of the video timing
signals is a line rate signal.
19. The apparatus as recited in claim 15 further comprising a softening filter having
as an input the subliminal data signal and producing as an output a filtered subliminal
data signal for input to the combiner as the subliminal data signal.
20. The apparatus as recited in claims 15, 16 or 19 further comprising an amplitude modulator
having as inputs the subliminal data signal and a gain control signal based upon a
human visual model and producing as an output an amplitude modulated subliminal data
signal as the subliminal data signal for input to the combiner.
21. The apparatus as recited in claim 15 wherein the pattern generator comprises:
a data pattern generator having as inputs the data to be embedded and the timing signals
and producing as an output a binary pattern;
a pseudo random binary sequence generator having as an input one of the timing signals
and producing as an output a random binary sequence;
a combination circuit having as inputs the binary pattern and the random binary sequence
and producing as an output the randomized binary pattern.
22. The apparatus as recited in claim 21 wherein the data pattern generator comprises
a circular shift register having as inputs the data and the timing signals and producing
as an output the binary pattern.
23. The apparatus as recited in claim 22 wherein the data pattern generator further comprises
a pattern encoder having the output from the circular shift register and the timing
signals as inputs and producing as an output the binary pattern.
24. The apparatus as recited in claim 23 wherein the data pattern generator provides a
plurality of bi-orthogonal binary patterns, with the one selected for output as the
binary pattern being determined by the output from the circulating shift register.
25. The apparatus as recited in claim 23 wherein the data pattern generator comprises
a Walsh encoder having as input the output from the circular shift register and producing
as an output the binary pattern selected from among a plurality of bi-orthogonal patterns.
26. The apparatus as recited in claim 15 wherein the combination circuit comprises an
exclusive OR gate having as inputs the binary pattern and the random binary sequence
and producing as an output the randomized binary pattern.
27. The apparatus as recited in claim 19 wherein the softening filter comprises:
a horizontal bandpass filter centered on the carrier frequency having as an input
the subliminal data signal and producing as an output a horizontally filtered subliminal
data signal; and
a vertical lowpass filter having as an input the horizontally filtered subliminal
data signal and producing as an output the filtered subliminal data signal.
28. The apparatus as recited in claim 20 further comprising:
a highpass human visual model filter having as an input the video signal and producing
as an output a highpass filtered video signal representing high spatial detail;
a lowpass human visual model filter having as an input the video signal and producing
as an output a lowpass filtered video signal representing local contrast; and
a combining circuit having as inputs the lowpass and highpass filtered video signals
and producing as an output the gain signal.
29. The apparatus as recited in claim 28 further comprising a temporal human visual model
filter having as an input the video signal and producing as an output a temporally
filtered video signal, the temporally filtered video signal being applied as another
input to the combining circuit so that the gain signal is a combination of the lowpass,
highpass and temporally filtered video signals.
30. The apparatus as recited in claim 20 wherein the amplitude modulator is inserted between
the modulator and the softening filter.
31. The apparatus as recited in claim 20 wherein the amplitude modulator is inserted between
the softening filter and the combiner.
32. The apparatus as recited in claims 15, 16, or 19 further comprising a forward error
correction circuit having as an input the data to be transparently encoded within
the video signal and producing as an output a forward corrected data signal coupled
to the input of the pattern generator.
33. An apparatus for extracting transparently embedded data from a video signal where
the embedded data is a randomized binary pattern modulated onto a carrier frequency
comprising:
means for demodulating the video signal about the carrier frequency with a random
binary sequence modulated carrier frequency to produce a broadband video signal; and
means for correlating the broadband video signal with a plurality of binary patterns
to recover the embedded data.
34. The apparatus as recited in claim 33 further comprising means for filtering the video
signal prior to the demodulating means to enhance the embedded data with respect to
the video content of the video signal.
35. The apparatus as recited in claim 34 wherein the filtering means comprises:
means centered on the carrier frequency for broadband filtering the video signal to
produce a first filtered video signal; and
means for comb filtering the first filtered video signal to produce the video signal
for input to the demodulating means.
36. A method of extracting transparently embedded data from a video signal where the embedded
data is a randomized binary pattern modulated onto a carrier frequency comprising
the steps of:
demodulating the video signal about the carrier frequency with a random binary sequence
modulated carrier frequency to produce a broadband video signal; and
correlating the broadband video signal with a plurality of binary patterns to recover
the embedded data.
37. The method as recited in claim 36 further comprising the step of filtering the video
signal prior to the demodulating step to enhance the embedded data with respect to
the video content of the video signal.
38. The method as recited in claim 37 wherein the filtering step comprises the steps of:
broadband filtering the video signal about the carrier frequency to produce a first
filtered video signal; and
comb filtering the first filtered video signal to produce the video signal for input
to the demodulating step.
39. An apparatus for extracting transparently embedded data from a video signal where
the embedded data is a randomized binary pattern modulated onto a carrier frequency
comprising:
a demodulator having as inputs a random binary sequence modulated carrier frequency
and the video signal and producing as an output a broadband video signal; and
a correlation receiver having as inputs the broadband video signal and timing signals
associated with the video signal for comparing the broadband video signal with a plurality
of binary patterns to recover as an output the embedded data.
40. The apparatus as recited in claim 39 further comprising a filter having as an input
the video signal and producing as an output a filtered video signal coupled to the
input of the demodulator, the filter enhancing the embedded data with respect to the
video content of the video signal.
41. The apparatus as recited in claim 40 wherein the filter comprises:
a broadband filter centered on the carrier frequency having as an input the video
signal and producing as an output a first filtered video signal; and
a field comb filter having as an input the first filtered video signal and producing
as an output the filtered video signal coupled to the input of the demodulator.
42. The apparatus as recited in claim 39 wherein the demodulator comprises:
a pseudo random binary sequence generator having as an input one of the timing signals
and providing as an output a random binary sequence;
a numerically controlled oscillator having as an input a control signal derived from
the one timing signal and providing as an output the carrier frequency;
a first modulator having as inputs the carrier frequency and the random binary sequence
and producing as an output a modulated carrier frequency; and
a second modulator having as inputs the video signal and the modulated carrier frequency
and producing as an output the broadband video signal.
43. The apparatus as recited in claim 39 wherein the correlation receiver comprises:
a sampler having as an input the broadband video signal and producing as an output
a sampled video signal;
a pattern buffer having as inputs the timing signals and providing as outputs in parallel
a plurality of binary patterns;
a plurality of correlation circuits in parallel, each having as inputs the sampled
video signal and a specific one of the plurality of binary patterns and producing
as an output a specific correlation coefficient; and
a magnitude comparator having as inputs the correlation coefficients from each correlation
circuit and producing as an output a binary data word representing the sign and value
of the greatest of the correlation coefficients, the binary data word being the embedded
data.